Light-emitting diode and the manufacturing method of the same

ABSTRACT

The specification discloses a light-emitting diode and the corresponding manufacturing method. A GaN thick film with a slant surface is formed on the surface of a substrate. An epitaxial slant surface is naturally formed using the properties of the GaN epitaxy. An LED structure is grown on the GaN thick film to form an LED device. This disclosed method and device can simplify the manufacturing process. The invention further uses the GaN thick film epitaxial property to make various kinds of LED chips with multiple slant surfaces and different structures. Since the surface area for emitting light on the chip increases and the multiple slant surfaces reduce the chances of total internal reflections, the light emission efficiency of the invention is much better than the prior art.

BACKGROUND OF THE INVENTION

[0001] 1. Field of Invention

[0002] The invention relates to a light-emitting diode and themanufacturing method for it. More particularly, it relates to alight-emitting diode and the corresponding fabrication method with alower manufacturing difficulty and cost.

[0003] 2. Related Art

[0004] The light-emitting diode (LED) uses the intrinsic property ofsemiconductors to emit light, whose principle is different from that ofa normal lamp. Therefore, the LED is called a clod light source.Moreover, the LED has the advantages of being durable, light,energy-efficient, and not having mercury. Therefore, the illuminationindustry likes LED's very much.

[0005] Generally speaking, the LED is usually formed from epitaxy of theIll-V family mixed crystal compounds such as GaP and GaN. Since theindex of refraction of the LED's is greater than the exterior and theconventional LED's are mainly cubic in shape, light beams generated bythe LED with an incident angle larger than the threshold angle will betotally reflected at the diode/air interface back into the diode. Thefour interfaces of the cubically symmetric diode crystal are parallel toone another, causing the above-mentioned light beams to totally reflectwithin the LED. As a result, the light-emitting efficiency of the LED ismuch lower than its internal quantum efficiency. A solution to thisdeficiency is to change the crystal shape of the LED.

[0006] In accord with the current semiconductor machining technology,the first example that has successfully used this method is disclosed inthe U.S. Pat. No. 6229160, a truncated inverted pyramid (TIP) LED.According to that patent, the side surfaces of the AlGaInP/GaP LEDcrystal are made into a pyramid shape so that the four interfaces arenot parallel to one another. This configuration can effectively guidethe beams out, increasing the light-emitting efficiency by a factor oftwo. However, the TIP LED is formed by direct mechanical machining. Thismethod can only apply to AlGaInP/GaP red diodes. It utilizes the featurethat a four-element material can be conveniently machined to form theTIP LED. The GaN LED's, on the other hand, are mostly epitaxy onsapphires. As the sapphires are very hard, mechanical machining isalmost impossible. There has not been any breakthrough in thisdirection.

[0007] The U.S. Cree, Inc. is successful in making TIP LED's using GaN.They use the property that machining for SiC is much easier than thatfor sapphires to polish the SiC substrate. Using this method, the GaNLED can be made into a TIP shape. However, the crystal lattices of GaNand SiC, and the SiC substrate will absorb ultraviolet (UV) light,affecting the light-emitting efficiency of the UV GaN LED. Nevertheless,the white-light LED based upon the UV GaN LED is believed to be an idealilluminating material in the next generation. Although directly usingthe GaN substrate to make the InGaN/GaN LED can be made into the TIPshape using mechanical machining, the slant surfaces formed bymechanical machining will contain a layer with residual stress after theInGaN/GaN epitaxy is grown on the GaN substrate. Such a layer absorbslight and is not easy to be removed. Therefore, it is harmful to theLED. Furthermore, the GaN substrate has a lower yield and a higher cost.Its market price is much higher than the SiC substrate and the sapphiresubstrate. Therefore, it is hard to be commercialized.

SUMMARY OF THE INVENTION

[0008] To solve the problems in the existing manufacturing procedures,the invention provides an LED and the manufacturing method thereof. AGaN thick film with a slant surface is formed on a substrate surface.Utilizing special properties of GaN epitaxy, an epitaxial slant surfaceis naturally formed. The GaN thick film is further grown with an LEDstructure, forming an LED crystal. Therefore, there is no need to useadditional mechanical machining to make an LED structure with a slantsurface.

[0009] The LED formed using the above method is comprised of a substratewith a GaN thick film formed on the surface and a diode structure formedon the GaN thick film. The side surface of the GaN thick film and thesubstrate surface have an angle naturally formed due to the specialcrystal property of GaN. The GaN thick film is a mixture of severalIII-V family compounds. For example, the Al_(X)Ga_((1-X-Y))In_(Y)N filmhas 0≦X,Y<1 and 0≦X+Y<1. The diode structure formed on the GaN thickfilm surface consists of an n-GaN-series III-V family compound and ap-GaN-series III-V family compound. In particular, the n-GaN-seriesIII-V family compound and the p-GaN-series III-V family compound are inelectrically communications with low-resistance ohmic contact electrodesto provide a forward bias. The diode structure further contains anactive layer between the n-GaN-series III-V family compound and thep-GaN-series III-V family compound as its light-emitting region.

[0010] Moreover, according to the disclosed method, the low-resistanceohmic contact electrodes of the n-GaN-series III-V family compound, theactive layer, and the p-GaN-series III-V family compound can be formedon the upper and lower sides of the LED. This means can shrink the sizeof the device, increasing the light emission efficiency and yield.

BRIEF DESCRIPTION OF THE DRAWINGS

[0011] The invention will become more fully understood from the detaileddescription given hereinbelow illustration only, and thus are notlimitative of the present invention, and wherein:

[0012]FIG. 1 is a flowchart of the disclosed manufacturing process;

[0013]FIG. 2 is a schematic view of the first embodiment;

[0014]FIG. 3 is a schematic view of the second embodiment; and

[0015]FIG. 4 is a schematic view of the third embodiment.

DETAILED DESCRIPTION OF THE INVENTION

[0016] The disclosed LED and manufacturing method utilizes the epitaxialgrowth characters of GaN to fabricate LED's. Based upon this, variouskinds of LED's with multiple slant sides, different structures, andbetter light emission efficiencies can be made.

[0017] We use FIG. 1 to explain the manufacturing procedure of theinvention. First, a substrate is provided (step 410). Afterwards, thesurface of the substrate is formed with a pattern for selectively areagrowing epitaxy. The area of the pattern is slightly larger than thesize of the desired device (step 420). An AlGaInN thick film with aslant surface is formed on the pattern of the substrate (step 430). Sucha slant surface is naturally formed as a result of the special propertyof the GaN epitaxy. The AlGaInN thick film is formed with a LEDstructure with the n-GaN-series III-V family compound and thep-GaN-series III-V family compound (step 440). Finally, a p-typelow-resistance ohmic contact electrode is formed on the surface of thep-GaN-series III-V family compound, and an n-type low-resistance ohmiccontact electrode is formed on the surface of the n-GaN-series III-Vfamily compound, finishing the LED chip (step 450). In particular, theLED structure further contains an active layer as the light-emittingregion. The surfaces of the n-GaN-series m-V family compound and thep-GaN-series III-V family compound are in electrical communications withthe low-resistance ohmic contact electrodes, providing a forward bias.The invention also contains the step of removing the substrate usinglaser, which simplifies the chip cutting process of cutting the crystal.The yield is thus increased, whereas the manufacturing cost is lowered.

[0018] The LED of the invention can have several kinds of structures.With reference to FIG.2, the first embodiment of the invention containsa substrate 100, an AlGaInN thick film 110 with a slant surface, and anLED structure. The AlGaInN thick film 110 is an epitaxy formed on thesurface of the substrate 100. The LED structure is comprised of ann-GaN-series III-V family compound 130, an active layer 150, and ap-GaN-series III-V family compound 140. The surface of the p-GaN-seriesIII-V family compound 140 has a combination of a transparent contactlayer (TCL) and a p-type low-resistance ohmic contact electrode 141. Thesurface of the n-GaN-series III-V family compound 130 has an n-typelow-resistance ohmic contact electrode 131. The n-GaN-series III-Vfamily compound 130, the active layer 150, and the p-GaN-series III-Vfamily compound 140 are formed in order on the surface of the AlGaInNthick film 110.

[0019] The invention can also use a transparent conductive substrate tomake the LED. In this embodiment, the low-resistance ohmic contactelectrodes of the n-GaN-series III-V family compound, the active layer,and the p-GaN-series III-V family compound can be formed on the upperand lower surfaces of the LED. This can minimizes the size of the devicewhile at the same time increasing the light emission efficiency andyield. Please refer to FIG. 3, where the structure contains: an n-typetransparent conductive substrate 200, an AlGaInN thick film 210 with aslant surface, an LED structure. One surface of the n-type transparentconductive substrate 200 has a combination of a TCL 220 and an n-typelow-resistance ohmic contact electrode 231. The AlGaInN thick film 210is an epitaxy formed on the other surface of the n-type transparentconductive substrate 200. The LED structure is comprised of ann-GaN-series III-V family compound 230, an active layer 250, and ap-GaN-series III-V family compound 240. The surface of the p-GaN-seriesIII-V family compound 240 has a combination of a p-type low-resistanceohmic contact electrode 241 and a reflective metal electrode 260.

[0020] In another structure of the invention, the substrate is removedto simplify the LED chip cutting process. This can simultaneouslyincrease the yield but lower the cost. A third embodiment of theinvention is shown in FIG. 4. The structure contains: an AlGaInN thickfilm 310 with a slant surface and an LED structure. The LED structure iscomprised of an n-GaN-series III-V family compound 330, an active layer350, and a p-GaN-series III-V family compound 340. The surface of then-GaN-series IIIl-V family compound 330 has an n-type low-resistanceohmic contact electrode 331. The surface of the p-GaN-series III-Vfamily compound 340 has a combination of a p-type low-resistance ohmiccontact electrode 341 and a TCL 320.

[0021] As described above, the substrate for the epitaxial growth of anAlGaInN thick film with a slant surface according to the invention canbe a sapphire, SiC, Si, GaAs, AlN, LiAlO2, and LiGaO2. The n-typetransparent conductive substrate can be an n-GaN, an n-ZnO, and ann-SiC. The method for the epitaxial growth of an AlGaInN thick film witha slant surface is the hydride vapor phase epitaxy (HVPE). The innerdiameter of the pattern for selectively area growing epitaxy is largerthan 150μm. The shape of the pattern can be a quadrilateral, hexagon, orcircle, which determines the shape of the natural slant surface of thethick film. The thickness of the AlGaInN thick film with a slant surfaceis above 20μm. Due to the properties of the GaN epitaxy, the bottomsurface of the GaN thick film and its side surface subtends an angle α,where 43°≦α≦62°. The p-type low-resistance ohmic contact electrode andthe n-type low-resistance ohmic contact electrode can be transparentlow-resistance ohmic contact electrodes. The p-type low-resistance ohmiccontact electrode can be a p-type transition metal oxide semiconductoror a mixture of a p-type transition metal oxide semiconductor and heavymetals. The LED structure further contains an active layer between then-GaN-series III-V family compound and the p-GaN-series III-V familycompound as the light-emitting region. The active layer can be adouble-heterostructure (DH), a single-quantum well (SQW) or amultiple-quantum well (MQW).

[0022] Certain variations would be apparent to those skilled in the art,which variations are considered within the spirit and scope of theclaimed invention.

What is claimed is:
 1. A manufacturing method of a light-emitting diode(LED) comprising the steps of: providing a substrate; forming a patternon a surface of the substrate for selective area epitaxy growth; forminga GaN thick film with a slant surface over the pattern using an epitaxygrowth method, wherein the slant surface is naturally formed as a resultof the properties of GaN and the upper surface of the GaN thick film isa plane with an area suitable for device uses; and forming an LEDstructure on the GaN thick film, wherein the LED structure contains ann-GaN-series III-V family compound and a p-GaN-series III-V familycompound, and p-GaN-series III-V family compound is in electricalcommunications with a p-type low-resistance ohmic contact electrode andthe n-GaN-series III-V family compound is in electrical communicationswith an n-type low-resistance ohmic contact electrode for providing aforward bias.
 2. The method of claim 1, wherein the GaN thick film is anAl_(X)Ga_((1-X-Y))In_(Y)N thick film with 0≦X,Y<1 and 0≦X+Y<1.
 3. Themethod of claim 1 further comprising the step of removing the substrate.4. The method of claim 1, wherein the method of forming the GaN thickfilm with a slant surface is the hydride vapor phase epitaxy (HVPE). 5.The method of claim 1, wherein the substrate is selected from the groupconsisting of sapphire, SiC, Si, GaAs, and AlN substrates.
 6. The methodof claim 1, wherein the substrate is a transparent conductive substrate.7. The method of claim 1, wherein the thickness of the GaN thick film isabove 20 μm.
 8. The method of claim 1, wherein the inner diameter of thepattern is greater than 150 μm.
 9. The method of claim 1, wherein thepattern has a shape selected from the group consisting of aquadrilateral, a hexagon and a circle.
 10. The method of claim 1,wherein the bottom surface and the side surface of the GaN thick filmsubtend an angle α, where 43°≦α≦62°.
 11. An LED device comprising: a GaNthick film with a slant surface formed using the epitaxial property; andan LED structure, which contains an n-GaN-series III-V family compoundand a p-GaN-series III-V family compound; wherein the n-GaN-series III-Vfamily compound is stacked on the surface of the GaN thick film and inelectrical communications with an n-type low-resistance ohmic contactelectrode, and the p-GaN-series III-V family compound is in electricalcommunications with a p-type low-resistance ohmic contact electrode forproviding a forward bias.
 12. The LED device of claim 11, furtherincluding the GaN thick film with a slant surface formed on a surface ofthe substrate by epitaxy.
 13. The LED device of claim 12, wherein thesubstrate is selected from the group consisting of sapphire, SiC, Si,GaAs, AlN, LiGaO₂ and LiAlO₂ substrates.
 14. The LED device of claim 11,wherein the GaN thick film is an Al_(X)Ga_((1-X-Y))In_(Y)N thick film,where 0≦X,Y<1 and 0≦X+Y<1.
 15. The LED device of claim 11, wherein thethickness of the GaN thick film is above 20 μm and its inner diameter ofthe pattern is greater than 150 μm.
 16. The LED device of claim 11,wherein the pattern has a shape selected from the group consisting of aquadrilateral, a hexagon and a circle.
 17. The LED device of claim 11,wherein the bottom surface and the side surface of the GaN thick filmsubtend an angle α, where 43°≦α≦62°.
 18. The LED device of claim 11,wherein the n-type low-resistance ohmic contact electrode and the p-typelow-resistance ohmic contact electrode are formed on the same side ofthe GaN thick film, the p-type low-resistance ohmic contact electrodebeing formed on the GaN thick film of the p-GaN-series III-V familycompound and the n-type low-resistance ohmic contact electrode beingformed on the surface of the p-GaN-series III-V family compound.
 19. TheLED device of claim 11, wherein the LED structure further contains anactive layer between the n-GaN-series III-V family compound and thep-GaN-series III-V family compound as a light-emitting region.
 20. TheLED device of claim 11, wherein the active layer is selected from thegroup consisting of a double heterostructure (DH), a single-quantum well(SQW) or a multiple-quantum well (MQW).